A large number of antenna applications require low-profile antenna arrays that can be flush-mounted in or on a structure. Such antennas are usually referred to as “conformal array antennas.” The designs available until now that are thin have been narrow band, permitting use only over a narrow range of frequencies. Conversely, those previously known antennas that are wide band have been thick, with excessive intrusion into, or protrusion from, the supporting structure.
Waveguide slots are one of the most common radiating elements used for low-profile array antennas. They are typically less than 0.25 wavelengths deep, but their bandwidth is only about 5 percent. Microstrip patch elements are another popular choice. They are even shallower than slot elements, but are also limited to about 5 percent bandwidth. In contrast, wide band radiating elements such as notches are usually about one wavelength deep.